Surfactants (e.g., polysorbate 80) or proteins in biopharmaceuticals can encapsulate endotoxin molecules into micelles. The LAL enzyme cannot access the lipid A, producing a false negative.
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Container closure systems (glass vials, pre-filled syringes, stoppers) can adsorb endotoxins over time. The liquid phase tests negative, but the endotoxin is physically present on the container wall. Surfactants (e
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